Heat-sensitive recording material

ABSTRACT

A HEAT-SENSITIVE RECORDING MATERIAL CONTAINING A THERMOSENSITIVE RECORDING LAYER COMPRISING HYDROPHOBIC THERMOPLASTIC PARTICLES DISPERSED IN A HYDROPHILIC BINDER AND IN UNDERLYING CONTACTING RELATION TO SAID RECORDING LAYER AN UNDERLAYER HAVING A HYDROPHILITY AND REMOVABILITY WITH WATER LESS THAN THAT OF SAID RECORDING LAYER AND WHICH CONTAINS AT LEAST ONE THERMOPLASTIC SUBSTANCE HAVING A HYDROPHOBIC CHARACTER AND A MELTING OR SOFTENING POINT SUCH THAT SAID SUBSTANCE REMAINS ADHERENT AFTER HEATING TO THE HEAT COALESCED HYDROPHOBIC THERMOPLASTIC PARTICLES CONTAINED IN THE HYDROPHILIC BINDER OF THE RECORDING LAYER. ACCORDING TO A PREFERRED EMBODIMENT THE INTERLAYER HAS BEEN PREPARED FROM A LATEX CONTAINING POLYMER PARTICLES WHICH COALESCE ON DRYING THE COATED LAYER AT ROOM TEMPERATURE. THE INTERLAYER MAY CONTAIN HYDROPHILIC PIGMENTS SUCH AS COLLOIDAL SILICA AND A HYDROPHILIC BINDER THAT IS PREFERABLY LESS SOLUBLE IN WATER THAN THE HYDROPHILIC BINDER OF THE RECORDING LAYER AND THE WEIGHT RATIO OF POLYMER PARTICLES RELATIVE TO THE HYDROPHILIC BINDER IS PREFERABLY AS LEAST 1:1.

HEAT-SNSITIVE RECORDING MATERIAL Filed Nov. 23, 1970 AUnited States Patent Ollce? 3,679,410 Patented July 25, 1972 Int. c1. 603e 5/04 U.S. Cl. 96-27 48 Claims ABSTRACT F THE DISCLOSURE A heat-sensitive recording material containing a thermosensitive recording layer comprising hydrophobic thermoplastic particles dispersed in a hydrophilic binder and in underlying contacting relation to said recording layer an underlayer having a hydrophility and removability with water less than that of said recording layer and which contains at least one thermoplastic substance having a hydrophobic character and a melting or softening point such that said substance remains adherent after heating to the heat coalesced hydrophobic thermoplastic particles contained in the hydrophilic binder of the recording layer.

According to a preferred embodiment the interlayer has been prepared from a latex containing polymer particles which coalesce on drying the coated layer at room temperature. The interlayer may contain hydrophilic pigments such as colloidal silica and a hydrophilic binder that is preferably less soluble in water than the hydrophilic binder of the recording layer and the weight ratio of polymer particles relative to the hydrophilic binder is preferably at least 1:1.

The present invention relates to the recording and reproduction of information and to recording materials for use in a recording method, based on information-wise heating 'of a heat-sensitive recording element.

The present application is a continuation-in-part of the patent application No. 608,571, now abandoned, led Jan. 11, 1967.

In the Belgian patent specification 656,713 a recording material is described which contains a heat-sensitive layer comprising thermoplastic polymer particles dispersed in a hydrophilic binder.

In the U.S. Pat. 3,476,937 a recording layer is described comprising a hydrophilic :binder incorporating hydrophobic thermoplastic particles in heat-conductive relationship with at least one light-absorbing substance wherein absorbed light is transformed into heat. Heat produced in such substance and conducted to the thermoplastic particles produces in the recording layer a decrease in water-permeability and Water-solubility.

According to an embodiment described in said U.S. patent specification for recording and producing a copy of an original, the image-wise differentiation in Watersolubility is utilized for removing the recording layer in the non-heated or insuiiiciently heated areas e.g. by washing away or degrading the hydrophilic binder. Thus, when the recording layer comprises a pigment or dissolved dyestuff a copy of the original is formed by applying the Washing away technique.

Dependent on the properties of the support for the recording layer an opaque or transparent copy of the original is produced.

The present invention is concerned with improvements in heat-sensitive recording materials which are capable of being used to record information in terms of a difference in the water-permeabilities of different areas of the recording layer, and is in particular concerned with recording processes wherein after the information-wise heating of the recording material the still water-permeable or relatively more water-permeable areas of the recording layer are removed by means of water or an aqueous liquid. The various refinements or developments above referred to, for instance, permitting a heat pattern to be generated internally of the recording material by irradiating this material, are compatible with the present invention and may be adopted in the performance thereof.

In order to obtain sharp copies of the original on applying the washing-away technique, a recording material is needed the recording layer of which strongly adheres to its base in the heated areas. Indeed, for selectively washing away the non-heated or insulciently heated portions of the recording layer in a small lapse of time, it may be required to rub the recording layer, e.g. with a spongelike element soaked with water. If the heated portions of the recording layer do not adhere appreciably more strongly to the base material than the non-heated portions, the rubbing of the recording layer in wet state or the tearing out of swollen non-heated portions may result in a damaging of the image or in a loss in image sharpness.

It has now been found that the wet removal of the nonheated portions of a heat-sensitive recording material can be effected more selectively when in the heat-recording process a heat-sensitive recording material is used comprising a heat-sensitive recording layer containing hydrophobic thermoplastic particles dispersed in a hydrophilic binder and which layer is in contacting relationship with an underlayer containing one or more thermoplastic substances having a hydrophobic character and a melting or softening point such that said substances remain adherent to the coalesced hydrophobic thermoplastic particles contained in the hydrophilic binder of the recording layer when melted or softened by the information-wise heating of the heat-sensitive recording material and wherein said interlayer is characterized by a lesser waterpermeability and removability with water than said recording layer.

It is preferred for the said interlayer to comprise hydrophobic thermoplastic substances having a softening or melting point equal to or lower than that of the hydrophobic thermoplastic polymer particles in the recording layer. The use of thermoplastic substances with a melting or softening temperature which is higher is not excluded, however, since in that case only a higher imaging temperature has to be applied.

During the exposure of a heat-sensitive recording material according to the invention, the hydrophobic thermoplastic polymer particles must be heated in such a degree that they coalesce in the exposed areas of the recording layer, and in order that the coalesced polymer particles will strongly adhere to the thermoplastic substance in the underlying layer, this substance has to be softened or melted by the same heat. The thermoplastic substance, moreover, must be sufciently hydrophobic to bind or to adhere to the hydrophobic thermoplastic polymer in the recording layer. If the interlayer is too hydrophobic, dtiiculties will be encounteded in obtaining a good ad hesion to it of the recording layer. A certain content of wetting agent and/or hydrophilic binder can be incorporated into the interlayer to provide a good anchorage. An improved vanchorage can also be obtained by electrostatically charging the interlayer and/or support before applying the composition for forming the recording layer.

According to a -lirst embodiment the interlayer on which the recording layer is formed comprises a dispersion of 3 thermoplastic polymer particles (i.e. a latex) in a continuous phase, e.g., a hydrophilic binder. The interlayer acting as a subbing layer contains preferably hydrophobic rthermoplasticpolymer. particles in a hydrophilic binding agent that is less soluble in water than the hydrophilic binding agent of the recording layer. For instance, the interlayer contains gelatin hardened to some degree with e.g. formaldehyde and the recording layer contains polyvinylalcohol. The binding agent for the hydrophobic polymerl particles contained in the interlayer may be water- Ainsoluble but is preferably less hydrophobic than said particles. A suitable binding agent is a copolymer of mainly Ahydrophobic vinyl monomers e.g. styrene, butadiene and vinylidene chloride and a minor amount of hydrophilic monomer or monomers e.g. methacrylic acid, itaconic acid Yand n-tert.butylacrylamide.

According to a second embodiment the interlayer is a thermoplastic polymer layer e.g. preparedfrom a latex containing hydrophilic pigment particles e.g. colloidal silica, optionally together with a hydrophilic binding agent. For instance the interlayer contains hydrophobic thermoplastic polymer particles dispersed in a binder which may be a latex (a so-called soft latex) the polymer particles of which coalesce and form a continuous phase on drying kthe coated layer at room temperature C.) together Ywith hydrophilic pigment particles e.g. zinc oxide, silica and titanium dioxide. A latex dispersion contains any necessary wetting agent for keeping the polymer particles dispersed: in aqueous or hydrophilic medium.

,A According to a third embodiment the interlayer essentially consists of coalesced hydrophobic thermoplastic f polymer particles. For example the interlayer is a poly` v ethylene layer applied from a polyethylene latex of which the polyethylene particles have been coalesced by heating above their melting temperature. f According .to a modification of that embodiment the interlayer is prepared from a soft latex (i.e. a latex the polymer particles of which have a melting or softening 'The interlayer when containingy a hydrophilic binding agent contains it in a ratio by weight with respect to the Qhydrophobic material preferably smaller than the ratio by weight of the hydrophilic binding agent to hydrophobic v thermoplastic particles contained in the recording layer.

The hydrophobic substances of the recording layer Aandinterlayer have preferably the same chemical structure but may have a different chemical structure provided they wet (i.e. adhere to) each other in fused or softened state, asis the case e.g. with polystyrene and polyethylene polymer particles.

In preferred combinations the hydrophobic substances of said layers are compatible (i.e. miscible) in fused state.

- As preferred hydrophobic substances Vthermoplastic polyw mer particles applied from a latex are used but layers applied from aqueous wax particle dispersions as e.g.fde scribed in the U.S. patent specification 3,156,183 are not excluded. I

' The U.S. patent specification 3,476,937 and the published Dutch patent application' 66/ 6,7 19 contain data relating to heat-sensitive recording layers which are applicable in carrying out the presentinvention and these documents should therefore ber read in conjunction herewith.

4 VBy the image-wise applied heat, the interlayer ismore i firmly bound to the recording layer in the heated areas than in the non-heated areas. This can be yexplained in terms of a so-called fusion-junctiony in said heated areas between said interlayer or self-supporting sheet and the recording layer. In other words the coalesced hydrophobic polymer particles .ofthev recording layer remain after the jinformation-wise heating adherent to the hydrophobic substance of the interlayer in corresponding with the information-wiseheated areas. The interlayer kmay be applied 4 directly to a support, in respect of which it possessesa proper adhesive power, or may be applied to a support which is precoated with one or more intermediate subbing layers in order to obtain at storage temperature a sufcient adhesion between said interlayer and the support.

Having stated in general the concepts of this invention a detailed description will now be made of the cornposition and structure of preferred heat-sensitive materials according to the invention and their use in heat-recording processes.

FIGS. 1 and 2 of the accompanying drawing are enlarged sectional views of representative types of heatsensitive materials according to the present invention.

As illustrated in FIG. 1 a particular heat-sensitive ma- 'terial according to the present invention contains:

A heat-sensitive recording layer 1 comprising a hydrophilic binder 2, dispersed hydrophobic thermoplastic polymer particles 3, and dispersed substances 4, which absorb copying light and transform said light into heat;

An interlayer (i.e. subbing layer) 5 comprising a hydrophilic binder and dispersed thermoplastic polymer particles having a melting or softening point which is lower than,

equal to or not substantially `higher than that of the parport.

Suitable subbing layers capable of adhering hydrophilic layers such as gelatin-containing layers to cellulose triacetate and polyethylene terephthalate supports are well known from the silver halide photographic art.

The hydrophilic binder of the recording layer and occasionally that of the interlayer may, e.g.,k constitute a hydrophilic natural colloid, a modified hydrophilic natural colloid, or a synthetic hydrophilic polymer or polycondensation product.r More particularly said binding agent may be selected from natural or modified natural hydrophilic colloids, e.g. gelatin, glue, casein, zein,v hydroxyethylcellulose, carboxymethylcellulose, methylcellulose, carboxymethyl hydroxyethylcellulose, gum arabic, sodium alginate and hydrophilic derivatives of such colloids. They may also be selected from synthetic hydrophilic polymers such as, e.g., polyvinyl alcohol, poly-N-vinylpyrrolidone, polyvinylamine, polyethylene oxide polymers, polystyrene sulphonic acid, polyacrylic acid and hydrophilic derivatives of such polymers. I The hydrophilic binder material for use in the record- 1 ng layer of the heat-sensitive recording 4materials accordmg to the present invention is preferably water-soluble at room temperature (20-25 C.). In this respect polyhl-vinylpyrrolidone, polyvinyl alcohol, polyethylene ox- 1de and gelatin containing a softening agent, e.g. urea,v

are preferred. n

When the interlayer contains a hydrophilic binder it does not necessarily mean that the interlayer in the nonformer being used in an linterlayer and the latter in the recording layer. The poly-N-vinylpyrrolidone is more water-soluble than gelatin at room temperature.

So, according to a preferred embodiment of the invention a completely transparent interlayer is used, which contains dispersed hydrophobic thermoplastic particles in a hydrophilic binder, which is less water-soluble than the hydrophilic binder of the recording layer.

Information about the kind and preparation of thermoplastic hydrophobic polymer particles suitable for use in the heat-sensitive recording layer as well as in the interlayer can be found, e.g. in the U.S. patent specification 3,476,937.

lThe recording layer contains preferably at least 50% by weight of the dispersion consisting of the hydrophilic binder and the hydrophobic thermoplastic polymer particles dispersed therein, and should be coated and dried in such conditions that it is water-permeable at a temperature, e.g., not substantially higher than room temperature. The polymer particles being solid at room temperature preferably soften between and 200 C. above room temperature. It is preferred to use in the recording layer and in the underlying interlayer polymers having a melting point or glass-transition temperature between 10 and 200 C. above room temperature.

More particularly are suitable, e.g. polyethylene and polyvinylidene chloride having a melting point of 110 and 190 C. respectively, and the following polymers with their respective glass-transition temperatureszpolystyrene (100 C.), polymethyl methacrylate (comprised between 70 and 105 C.), polyethyl methacrylate (50 C.), polyvinyl chloride (near 70 C.), polyacrylonitrile (near 100 C.), poly-N-vinylcarbazole (200 C.).

The polymer selected for the interlayer has preferably a melting point or glass-transition temperature below that of the polymer in the recording layer or not substantially higher, e.g. has a melting point in the range of C. above and 20 C. below the melting point of the coalesable polymer particles in the recording layer.

As is known, the glass-transition temperature can be lowered by the addition of some substances called plasticizers. More particulars about suitable plasticizers and the glass-transition tempereature of homoand copolymers can be found e.g., in Georges Champetier, Chimie Macromolculaire-Gnralits, Librairie Armand Colin- Paris Verne, pp. 194-198. It appears therefrom that a range of glass-transition temperatures can -be obtained, a given glass transition temperature :being determined by the ratio of the monomers of condensation reagents used during the copolymerisation or copolycondensation. Thermoplastic hydrophobic polymers covering a wide range of molecular weights may be used in materials according to the present invention both in the recording layer and in the interlayer. Polymers possessing a molecular weight ranging from 5000 to 1,000,000 are preferred.

Polyethylene possessing a molecular weight of 15,000 to 50,000 was found to very suitable. Of course, mixed dispersions of polymer particles may also be used and in the case of the recording layer different polymer particles may occasionally contain reaction components, which at the moment of diffusing into one another as a result of the application of heat or pressure react with one another, e.g., with resulting formation of colour.

Preferred hydrophobic thermoplastic homopolymers and copolymers suitable for the manufacture of a recording layer and/or interlayer according to the present invention are applied as an aqueous dispersion containing a hydrophilic binding agent. The aqueous dispersion of the homopolymer or copolymer is prepared preferably by radical polymerisation in emulsion of one or more polymerisable monomers according to known techniques, e.g., those described by W. Srenson and T. W. Campbell, Preparative Methods of Polymer Chemistry, Interscience Publishers, New York (1961). In the radical polymerisation use is made of dispersing agents such as those described by K. Laux, Die Grenztlchenaktiven Stole in Winnacker-Kchlers Chemische Technologie, Carl Hanser Verlag, Munich (1960), pp. -242.

Aqueous dispersions of polymers prepared by dispersing a solution of a water-insoluble polymer in a waterimmiscible volatile solvent in an aqueous solution of a hydrophilic binding agent are also considered. As solvents may be mentioned, e.g., chlorinated hydrocarbons such as methylene chloride and trichloroethylene.

Further, polymer dispersions, which are appropriate for use in the recording layer and/or interlayer of a material according to the present invention can be obtained by mechanically dispersing in water nely divided polymer particles, preferably with the help of surfactants and/ or hydrophilic protective colloids such as polyvinyl alcohol and gelatin. Latices obtained by emulsion polymerisation are preferred. In this polymerisation technique one or more monomers are dispersed by stirring them to very fine droplets in the presence of water, emulsiers such as soaps, ammonium oleate, sulphonated fatty alcohols and the like, protective colloids such as carboxymethylcellulose, polyvinylalcohol and the like, a buffering system, a surfactant and a water-soluble catalyst, e.g., hydrogen peroxide or a persulphate. The polymer is obtained as a stable dispersion of polymer particles in water.

The size of the polymer particles in dispersion may vary from 0.01/1. to 50p. However, in connection with the recording layer it is noted that the larger the particles the less is the resolving power. Very good results are obtained with dispersions the dispersed polymer particle size of which varies from 0.05# to 20g. Dispersions wherein the size of the dispersed particles varies from 1n to lmp. are considered as colloidal systems. A colloidal system the continuous phase of which is formed by water (dispersing medium) and the dispersed phase of which is formed by particles having a size varying from 1 to 0.00111. is called a hydrosol. Good results are obtained when using hydrosols the polymer particles of which are not greater than 0.1,u.

The ratio by weight of thermoplastic polymer particles to hydrophilic binder in the recording layer as well as in the interlayer (if the latter contains a hydrophilic binder) is preferably greater'than 1:1, more preferably greater than 3:2. For instance when using gelatin as the binding agent in the interlayer the ratio by weight of gelatin to polymer particles is 1 to 3 and when using polyvinylalcohol 1 to 6. The amount by weight of thermoplastic polymer particles comprised in the recording layer and an interlayer containing such particles is preferably in the range of 0.5 g. to 10 g./sq. m.

Recording layers and interlayers used in the present invention preferably each have a thickness from 0.5,u. to 10/1..

According to a preferred embodiment, the recording layer of the recording material contains, colored substances e.g. pigments or dyes preferably in water-insoluble state. These substances may absorb copying light and transform said light into heat. Preferred substances absorbing visible light and infrared light and converting said light into heat are dark coloured or black pigments, e.g., nely divided carbon black, graphite, prussian blue, oxides, sulphides or carbonates of heavy metals, particularly of those heavy metals having an atomic Weight between 45 and 210, such as manganese or lead sulphide or these heavy metals themselves in finely divided state such as silver, bismuth, lead, iron, cobalt, and nickel.

According to a particular embodiment the heat-sensitive material can be made sensitive to light of a limited region of the visible spectrum. This can be done by incorporating into the heat-sensitive layer coloured substances, which absorb light of a part of the visible spectrum and convert that light into heat as described in the published Dutch patent application 6606719. A thermographic layer spectrally sensitized in that way can be used for recording coloured originals in terms of differences in water-solubility and wash-off removability.

It is to be understood that mixtures of said coloured substances can be used too, so that light of the whole "visible spectrum is absorbed. The said substances need not necessarily absorb in the range of the visible spectrum alone, they may also absorb to some extentv infrared light, which light is normally produced to some extent by llash lamps. i

Coloured substances or mixtures of said substance when used for optical sensitization of the thermographic 'recording layer preferably absorb light corresponding to `Said dyes can be used and dispersed as well as in dissolved form. The substances absorbing light and converting 1t into heat are preferably present in the recording layer in a concentration providing an optical density of at least l Vwhen direct exposure is applied, and in a concentration providing an optical density of 0.25 to 0.80 when the recording material is used in a reectographic exposure technique. When in dispersed form, the copying light ab- ,Y sorbing substances have preferably a particle size not greater than 0.1M. l

. The information-Wise heating of the recording material may proceed according to various ways.

`Acocrding to a common heat-recording process the heat'accumulated in the image areas of an original by infra-red irradiation is used to produce the necessary image differentiation in the heat-recording layer. In that heating process the recording layer does not contain pigments or dyes that are infra-red absorbing or when pigments or dyes are present they absorb that radiation only to a minor extent. n

Another Yprocedure which has proved to give very good results, is to use a type of recording material according to the present invention, wherein the recording layer con- ,contact-exposure as well as reflex exposureV can be applied. When applying a reilex copying method, the intensity of exposure, the concentration of substances absorbing copying light and the thermoplastic polymer particles present in the recording layer are chosen in such a way, that the heating resulting from the absorption of the light rays directed to the original and strikingundifferentially the heat-sensitive layer causes at most (pracftic'allyno or) only aslight loss of water-permeability and/or water-solubility in the heat-,sensitive recording layer. In other words, the image-wise heat resulting from the image-wise reflected light must produce in the record-l ingY layer a practically useful level of differentiation in swelling power or solubility in water.

A ccording to a particular embodiment, an image of heat-absorbing material is produced in the interlayer or recording layer by means of light-sensitive silver halide contained in both or one of said layers. The said silver halide is image-wise lexposed and developed. The silver image obtained acts as heat-absorbing image for producing by an overall exposure to light, e.g. infra-red light,

' the desired useful differentiation of swellability or solubility in water. v kFor reex exposure the support and'different layers of therecording material should obviously be sutliciently 8. transparent. When applying a transmission or contact printing process, however, the recording layer or any layer orsupport of the recording material may be opaque as well as transparent. In order to prevent lateral diffusion of heat and loss of image sharpness the exposure time preferably does not exceed 10'*1 sec.

Suitable radiation sources producing copying light of high intensity in a very small lapse of time and which are very suitable for application with recording materials containing light-absorbing substances converting Ythat light into heat are the so-called ash lamps. Good results are obtained with xenon gas discharge lamps, which can supply a light energy of V100 to 1000 watt.sec. in a time interval of 10-5 to 10-2 seconds. These Hash-lamps emit a greater part of energy as visible light than as infraredy light. Details about a copying apparatus containing such a discharge lamp can be found in Belgian'patent specification No. 664,868.

p Evidently gas discharge lamps with a lower energy output can be used if the emitted energy is focused onto a relatively small heat-sensitive area. So, e.g., a gas disn charge lamp with an energy output of 40 watt.sec. is

suited for copying 6 cm. x 6 cm. x 9 cm. originals on heatsensitive materials as described in the present invention. For materials having an optical density of at least l resulting from the presence in the recording layer of lightabsorbing substances, a light-energy ofk at least 0.1 watt.sec. per sq. cm. will be required for the desired image diierentiation. In practice an exposure of 0.3 watt.sec. per sq. cm. will provide satisfactory results. It is further self-explanatory that exposure may be progressive and intermittent. In other words the original may be scanned,

t e.g., by a high-intensity light spot rapidly line-wise scanning the original, or may be progressively exposed through a laterally moving slit wherein, e.g., copying light of a tube-like radiation source is focused.

It is evident that the heat-sensitive recording material, before or during the creation of the image-wise heat differentiation, can be subjected to overall heating to a certain temperature below the temperature at which a substantial decrease in swelling or solubility in water takes place. Y

After producing the image-wise differentiation in waterpermeability and wash-off removability of the recording layer the exposed material is processed by washing away the unexposed areas or by swelling the unexposed portions and removing them by tearing out with simultaneous transfer to a receiving material, e.g., a porous paper sheet. f

The following examples illustrate the present invention.

EXAMPLE l A poly(ethylene terephthalate) support of 0.1 mm. thickness provided with a subbing layer for gelatin is coated with the following composition pro rata of 30 g. per sq. m.:

The interlayer thus obtained is dried at 30 C.

On this layer a heat-sensitive layer, for use in a washingaway development by rubbing with `a cotton pad soaked with water of 20 C., is coated pro rata of 30 g. per sq. m. from the following composition:

G. aqueous solution of polyvinyl alcohol 45 40% aqueous dispersion of polyethylene as described 5 above I 60 Water 320 Aqueous carbon dispersion containing per 100 g. 53 g. of carbon (average particle size 0.1M), 23 g. of water, 18 g. of glycol and 6 g. of nonylphenyl poly- 10 ethylene oxide y 8 3% aqueous solution of the sodium salt of tetradecyl sulphate 25 After drying, the material is contact-exposed through a negative transparency being a reproduction of a printed text. The exposure is carried out by means of a xenon gas discharge lamp placed at a distance of 4 cm. of the recording layer and having a capacity of 1000 watt.scc., producing light in a time of 175000 sec.

After exposure the recording layer is rubbed with a cotton pad wetted with water of C., in this way removing the non-exposed and still water-permeable parts of the recording la'yer.

EXAMPLE 2 A poly(ethylene terephthalate) support of 0.1 mm. thickness provided with a subbing layer for gelatin is coated with the following composition pro rata yof g./sq. m.:

Exposure and development occur as described in the foregoing Example 1.

EXAMPLE 3 To a paper support coated with polyethylene and weighing 120 g./sq. m. an interlayer is applied from the following composition pro rata of g./sq. m. and then dried at 30 C.

10% aqueous gelatin 200 aqueous dispersion of polyethylene (see Example 1) 160 Water 120 10% aqueous saponine 20 aqueous solution of the sodium salt of the condensation product of oleic acid and methyl taurine 20 4% aqueous formaldehyde 10 Polyethylene glycol with an average molecular weight of 20,000 l0 On this layer a heat-sensitive layer is coated pro rata of 30 g./sq. m. from the following composition:

G. 20% aqueous solution of polyethylene glycol with an average molecular weight of 200,000 200 40% aqueous dispersion of polyethylene (see Example 1) 80 Water 145 Aqueous carbon dispersion (see Example 1) 40 3% aqueous solution of sodium tetradecylsulphate 25 10 Recording and development occur as described in Example l.

EXAMPLE 4 A poly(ethylene terephthalate) support of 0.1 mm. thickness is coated with the following solution pro rata of 15 g./sq. m.:

40% aqueous dispersion of polyethylene as described in Example l 1 50 20% aqueous dispersion of polyethyl acrylate (soft latex) i 50 30% aqueous dispersion of silica having a particle size of 25 mm. 50 Water 750 Ethanol After drying at 60 C., the subbing layer obtained is coated with a heat-sensitive layer from the following composition in a proportion of 20 g./sq. m.:

G. 10% aqueous solution of polyvinylpyrrolidone having an average molecular weight of 30,000 170 40% aqueous dispersion of polyethylene as described in Example 1 195 Aqueous carbon dispersion containing per 100 g.: 16 g. of carbon and 2 g. of low viscous poly(N vinylpyrrolidone) 50 Water 3% aqueous solution of the sodium salt of tetradecyl sulphate 65 After drying at 50 C., the material obtained is exposed and developed as in Example 1.

EXAMPLE 5 To a poly(ethylene terephthalate) support of 0.1 mm. thickness the following composition is applied pro rata of 20 g./sq. m.:

G. 40% aqueous dispersion of polyethylene described in Example 1 50 20% aqueous dispersion of copoly(vinylidene chloride/N butylmaleimide/itaconic acid) (83/ 15/2) Water y 750 30% aqueous dispersion of silica having a particle size of 25 mm. 50 Ethanol 100 After drying at i60" C., the subbing layer obtained is coated with a heat-sensitive layer as described in Example 4. After drying again, the material obtained is exposed and developed as in Example 1.

EXAMPLE 6 EXAMPLE 7 A poly(ethylene terephthalate) support of 0.1 mm. thickness provided with a subbing layer for gelatin is 1 1 -coated for forming an interlayer with the following composition pro rata of 30 g. per sq. m.:

% aqueous gelatin solution 300 40% aqueous dispersion of polyethylene having a particle size of less than 0.1/u and an average molecular weight comprised between 15,000 and Water 240 10% aqueous saponine 40 3% aqueous solution of the sodium salt of the condensation product of oleic acid and methyltaurine 40 4% aqueous formaldehyde 20 The interlayer thus obtained is dried at-30" C.

On this layer. a heat-sensitive layer, for use in a washing-away.` development by rubbing with a cotton pad soaked with water of C., is coated pro rata of 30 g. per sq. m. from the following composition:

G. 10% aqueous solution of polyvinyl alcohol 60 40% aqueous dispersion of polyethylene as described above 60 Water 320 Aqueous carbon dispersion containing per 100 g. 53 g. of carbon (average particle size 0.1M), 23 g. of Water, 18 g. of glycol and 6 g. of nonylphenyl polyethylene oxide 3% aqueous solution of the sodium salt of tetradecyl sulphate After drying, the material is contact-exposed through a negative transparency being a reproduction of a printed text. The exposure is carried out by means of a xenon gas discharge lamp placed at a distance of 4 cm. of the recording layer and having a capacity of 1000 watt.sec., producing light in a time of 175000 sec.

After exposure the recording layer is rubbed with a cotton pad wetted with water of 20 C., in this way removing selectively the non-exposed and still water-permeable parts of the recording layer.

EXAMPLE 8 To a poly(ethylene terephthalate) support of 0.1 mm. thickness the following composition is applied pro rata of 20 g./sq. rn.:

G. aqueous dispersion of polystyrene (average particle size 0.13p. and average molecular weight 50,000) 70 20% aqueous dispersion of copo1y(vinylidene chloride/N butylmaleimide/itaconic acid) (83/15/ 0 2) 5 Water 750 30% aqueous dispersion of silica having a particle size of 25 nrn 50 Ethanol L 100 After drying at 60 C., the subbing layer obtained is coated with a heat-sensitive layer as described in Example 4. After drying again, the material obtained is exposed and developed as in Example 1.

EXAMPLE 9 A poly(ethyleneterephthalate) support provided at both sides with a semi-transparent coating containing silica to give it the properties of a drafting film (prepared as described furtheron) was provided with a subbing layer of the following composition in a ratio of 15 g. per sq. m.:

Water g 746 Colloidal silica having an average particle size 0f S-nm. g 17 40% by weight aqueous dispersion of polyethylene having a particle size of less than 0.1 and an average molecular weight comprised between 12 15,000 and 30,000, melting point 110 C. ml by weight aqueous dispersion ofthe copolymer of styrene, butadiene, acrylonitrile and methacrylic acid (45/33/7/15% by weight) ml-- 4 30% by weight aqueous dispersion of colloidal silica of an average particle size of 0.025 nm. ml-- Ethanol ml The subbing layer thus obtained was dried at 50 C.

To the dried subbing layer a thermosensitive recording layer was applied in a ratio of 20 g. per sqm. from the following composition:

Water ml 212 20% by weight aqueous poly-N-vinylpyrrolidone solution (average molecular weight 30,000) ml 75 20% by weight aqueous dispersion (latex) of polyethylene prepared as described hereinafter ml 190 Aqueous carbon dispersion containing per 100 g.:

16 g. of carbon black and 2 g. of low viscous poly- N-vinylpyrrolidone) ml 330 30% by weight aqueous dispersion of silica (average particle size 0.025 nm.) ml 75 Ethylene glycol g 3 Ethanol ml 115 After drying, the material was contact-exposed through a negative transparency being a reproduction of a printed text. The exposure was carried out by means of a xenon gas discharge lamp placed at a distance of 4 cm. of the recording layer and having a capacity of 1000 watt.sec., producing light in a time of J000 sec.

After exposure the recording layer was rubbed with a cotton pad wetted with water of 20 C., in this way removing the non-exposed and still water-permeable parts of the recording layer.

Preparation of polyethylene latex In a 400 ml. metal pressure tube were placed:

Partly oxidized polyethylene prepared according to United Kingdom patent specification No. 997,135

tiled Oct. 25, 1963 by W. R. Grace & Co., by the oxidation of polyethylene (average molecular weight: 7000, crystalline melting point: 12S-130 C., acid number: 26-30) g 40 n-Hexadecyloxy-decycloxyethylene g 12.4 Water ml The pressure tube was sealed and rotated at 30-40 r.p.m. and heated at -200 C. for 1 hour in order to make a latex dispersion. Then the tube was allowed to cool slowly to room temperature. Yield: 200 ml. of a slightly beige latex of pH 9.

Preparation of the drafting lm 35 g. of very pure crystalline silicon dioxide having an average particle size of 5 mm. and 3.5 g. of monobutylphosphate were dispersed for 4 hours in 140 ml. of 1,2' dichloroethane.

The following components were then added consecutively to the resulting dispersion:

The resulting mixture was stirred for 3 hours and filtered.

The mixture was then diluted with 1,2-dichloroethane `to a concentration of approximately 20 g. of solids in 100 ml. A ml. of methyl polysiloxane was added as levelling agent per 100 ml. of lacquer composition.

This lacquer composition was applied at both sides of a polyethylene terephthalate lm support which was subbed at both sides with a :layer of a copolymer of vinylidene chloride, Ntert.butylacrylamide, n-butylacrylate, and N-vinylpyrrolidone (ratios by weight: 70:23:3:4).

The lacquer composition was applied in such a way that, after drying at 100 C. the resulting layer had a thickness of approximatively p.

The thus obtained drafting film was at one side coated with the subbing layer and thermosensitive layer as described above.

EQMPLE 10 To a poly(ethylene terephthalate) support of 0.1 mm. thickness the following composition for forming a subbing layer was applied pro rata of 13 g. per sq. m.:

IAfter drying at 50 C. the obtained subbing layer was coated with the following composition for forming a thermosensitive layer:

Water 432 Pigment Red 146 (C I. 11,000), an aqueous dispersion of a monazo pigment of a 3-hydroxy-2-naphthoic arylide sold under the trade name Permanent Carmin FBB Colanyl Teig by Farbwerke Hoechst AG Frankfurt (M), Hoechst, Federal Republic of Germany Pigment Yellow 83 (C.I. 20,000), an aqueous dispersion of a yellow disazo pigment dye sold under the trade name Permanent Gelb HR Colanyl Teig by Farbwerke Hoechst AG, Frankfurt '(M), Hoechst,

Federal Republic of Germany 40% by Weight aqueous dispersion of polyethylene having a particle size of less than 0.1,u and an average molecular weight comprised between 15,000

and 30,000 by weight aqueous solution of poly-N-vinylpyrrolidone (average molecular weight 30,000) 5% by Weight aqueous solution of caseine 5% by weight aqueous solution of a lwetting agent:1 30% by weight aqueous dispersion of colloidal silica having an average particle size of nm Ethanol 1 Formula After drying at 50 C. the heat-sensitive layer was brought in contact with the infrared absorbing indicia of a printed text on paper and exposed to infrared radiation in an apparatus known as a Thermographic Secretary Copying Machine marketed by Minnesota Mining and Manufacturing Company, St. Paul, Minn., U.S.A. Due to the selective absorption of the infrared rays in the infrared absorbing indicia of the original, and the transfer of the heat produced therein into the thermosensitive recording layer, the latter obtained an image-wise decrease in water-permeability and could be selectively washed off 14 in the unheated portions. The non-heated portions were washed oi with a soft rotating roller of foamed rubber wetted with water at room temperature.

A positive coloured reproduction of the printed text legible through the transparent support and suited for over-heat projection was obtained.

EXAMPLE 11 To a subbed poly(ethylene terephthalate) support of 0.1 mm. thickness containing a semi-transparent coating as described in Example 9 a subbing layer for a thermosensitive layer was applied, the coating composition of the subbing layer being the following:

Water 756 40% by weight aqueous dispersion of polyethylene having a particle size of less than 0.1# and an average molecular weight comprised between 15,000

and 30,000 40 351% by weight aqueous dispersion (latex) of a copolymer of butadiene, styrene, acrylonitrile and methacrylic acid (45:33:7:l5% by weight) 4 30% aqueous dispersion of colloidal silica having an average particle size of 25 nm. 100

Ethanol The coating proceeded at a ratio of 15 g. per sq. m.

The subbing Ilayer thus obtained was coated with the composition of a thermosensitive layer in a ratio of 20 g. per sq. m.:

by Weight aqueous solution of a wetting agent: 1

30% aqueous dispersion of colloidal silica having an average particle size of 25 nm ml-- 82 Ethanol ml-- 82 1 Formula After drying at 50 C. the recording material was image-wise heated and developed as described in Example 10. A positive green image on a semi-transparent support was obtained.

We claim:

1. In a thermographic method of recording information by the steps of exposing a heat-sensitive recording material comprising a heat-sensitive water-permeable recording layer containing hydrophobic thermoplastic particles dispersed in a continuous phase of a hydrophilic binding agent soluble in an aqueous liquid to heat applied in a pattern according to said information, said heat `being applied in an amount sul'licient to coalesce said hydrophobic thermoplastic particles and thereby reduce the water-permeability of said layer in the heated areas thereof, and treating said exposed material with an aqueous liquid to remove the unheated areas of the recording layer, the improvement of increasing the resistance to removal of the heated portions of said recording layer' by providing in underlying contacting relation to said recording 1layer an underlayer which contains at least one thermoplastic substance havin-g a hydrophic character and a melting or softening point such that said substance remains adherent to the coalesced hydrophobic thermoplastic particles contained in the hydrophilic binder of the recording layer upon the information-wise heating of the heat-sensitive recording material, and wherein said interlayer is characterized fby a lesser water-permeability and removability with water than said recordin-g layer.

2. A method according to claim 1, wherein said interlayer comprises a dispersion of thermoplastic polymer particles in a continuous phase of hydrophilic binder.

3. A method according to claim 1, wherein said interlayer contains as the thermoplastic substance hydropho'bic thermoplastic polymer particles in a hydrophilic binding agent that is less soluble in water than the hydrophilic binding agent of the recording layer.

4. A method according to claim 1, wherein said interlayer comprises a continuous phase of hydrophobic thervmoplastic polymer containing hydrophilic pigment particles.

5. A method according to claim 4, wherein said interlayer includes a hydrophilic binding agent for said pigment particles.

6. A method according to claim 4, wherein said interlayer has been prepared from a latex the polymer paryticles of which coalesce on drying the coated layer at room temperature and which contains optionally hydrophilic pigment particles.

7. A method according to claim 1, wherein said interlayer consists essentially of coalesced hydrophobic -thermoplastic polymer particles.

8. A method according to claim 2, wherein said interlayer contains a hydrophilic 'binding agent in an amount smaller than contained in the recording layer.

9. A method according to claim 1, wherein said interlayer contains a hydrophobic thermoplastic substance that has a chemical structure identical to that of the thermoplastic hydrophobic polymer particles contained in the recording layer.

1t). method according to claim 1, wherein said interlayer contains a hydrophobic thermoplastic substance that has a chemical structure different from the hydrophobic thermoplastic polymer particles contained in the recording layer but which wet or adhere to each other in fused or Vsoftened state.

. at least one substance, which converts absorbed electromagnetic radiation into heat energy, said recording layer is information-wise exposed to electromagnetic radiation the intensity and duration of which are such that in consequence of the absorption thereof by said substance a record is formed in terms of a different in water-solubility or r.swelling power in water\of different portions of the recording layer, which recording layer after the exposure is treated with an aqueous liquid in order to remove the non-exposed portions of the recording layer.

13. A method according to claim 1, wherein the information is recorded by heat-transfer from the image markings of an original which is held in contact with the recording layer during the exposure of the original to electromagnetic radiation heating the image markings.

14. A method according to claim 1, wherein the proportion in the recording layer of said polymer particles relative to the hydrophilic binder, has a weight ratio of at least 1:1.

15. A method according to claim 2, wherein the hydrophobic polymer particles and hydrophilic binder are present in the interlayer in a weight ratio of at least 1:1.

16. A method according to claim 1, wherein a hydrophilic binding agent is present in the recording layer which binding agent is soluble in water at room temperature.

17. A method according to claim 2, wherein `said polymer particles range in size from 0.1M. to 50p.

18. A method according to claim 2, wherein said polymer particles are latex polymer particles.

19. A method according to claim 2, wherein said particles are polyethylene particles.

20. A method according to claim 12, wherein a ashv lamp is said radiation source.

21. A method according to claim 12, wherein said informationwise irradiation of the recording layer is applied for a period of less than 10-1 second.

22. A method according to claim 12, wherein said informationwise irradiation of the recording material is applied for a period of time between 10-2 and 10-5 second.

23. A method according to claim 12, wherein the intensity of the radiation incident upon the recording material is at least 0.1 watt. sec. per sq. cm.

24. A method according to claim 12, wherein the recording material is exposed to light through a sheet bearing a visible image.

25. A method according to claim 12, wherein the recording material is exposed to light through a sheet bearing a visible image.

26. A method according to claim 1, wherein the recording layer contains a dark coloured or black pigment uniformly distributed in said layer.

27. A method according to claim 1, wherein the recording layer contains a dark coloured or black pigment uniformly distributed in said layer in such an amount that the recording layer possesses an optical density of at least 1.

28. A method -according to claim 25, wherein the recording layer contains a dark coloured or black pigment uniformly distributed in said layer in such an amount that the recording layer possesses an optical densitycomprised between 0.25 and 0.80.

29. A method according to claim 2, wherein the said polymer particles possess a melting or Vsoftening kpoint,

equal to or lower than that of the polymer particles in the recording layer.

30. A method according to claim 1, wherein the recording layer after the information-wise heating is treated with an aqueous liquid or water, whereby the portions of the recording layer correpsonding with the non-heat-exposed areas are washed away thus forming a relief image.

31. A method according to claim 1, wherein the nonheated portions of the recording layer are transferred a hydrophobic character and a melting or softening point such that said substance remains adherent after heating to the heat coalesced hydrophobic thermoplastic particles contained in the hydrophilic binder of the recording layer.

33. A heat-sensitive recording material according to claim 32, wherein said underlayer comprises particles of a hydrophobic thermoplastic polymer in admixture with hydrophilic material, said underlayer having a hydrophility less than that of said recording layer, and said polymer particles having a softening temperature not higher than that of the polymer particles of the recording layer and being adapted when molten to fuse compatibly with the polymer particles of the recording layer when molten.

34. A heat-sensitive recording material according to claim 33, wherein the interlayer comprises a dispersion of 1 7 thermoplastic polymer particles in a continuous phase of hydrophilic binder.

35. A heat-sensitive recording material according to claim 34, wherein the interlayer contains as thermoplastic substances hydrophobic thermoplastic polymer particles in a hydrophilic binding agent that is less soluble in water then the hydrophilic binding agent of the recording layer.

36. A heat-sensitive recording material according to claim 33, wherein the interlayer comprises a continuous phase of hydrophobic thermoplastic polymer containing hydrophilic pigment particles.

37. A heat-sensitivity recording material according to claim 33, wherein the interlayer has been prepared from a latex the polymer particles of which coalesce on drying the coated layer at room temperature and which contains optionally hydrophilic pigment particles.

38. A heat-sensitive recording material according to claim 33, wherein the interlayer consists essentially of coalesced hydrophobic polymer particles.

39. A heat-sensitive recording material according to claim 34, wherein the interlayer contains a hydrophilic binding agent in an amount smaller than contained in the recording layer.

40. A heat-sensitive recording material according to claim 33, wherein the interlayer contains a hydrophobic thermoplastic substance having a chemical structure which is identical to that of the thermoplastic hydrophobic polymer particles contained in the recording layer.

41. A heat-sensitive recording material according to claim 33, wherein the interlayer contains a hydrophobic thermoplastic substance having a chemical structure different from the hydrophobic thermoplastic polymer particles contained in the recording layer but which wet or adhere to each other in a fused or softened state.

42. A heat-sensitive recording material according to claim 33, wherein the interlayer contains a hydrophobic thermoplastic substance(s) that is compatible in fused state with the hydrophobic thermoplastic particles of the recording layer.

43. A heat-sensitive recording material according to claim 33, wherein the recording layer contains in heat-conductive relationship with said polymer particles at least one substance, which converts absorbed electromagnetic radiation into heat energy.

44. A heat-sensitive recording material according to claim 43, wherein said substance is carbon black.

4S. A heat-sensitive recording material according to claim 33, wherein the recording layer contains coloured pigments or dyes.

46. A heat-sensitive recording material according to claim 33, wherein in the recording layer said polymer particles are present in the hydrophilic binder in a weight ratio of at least 1:1.

47. A heat-sensitive recording material according to claim 34, wherein the interlayer comprises the hydrophobic polymer particles and hydrophilic binder in a weight ratio of at least 1:1.

48. A heat-sensitive recording material according to claim 33, wherein the recording layer and the interlayer contain latex polymer particles.

References Cited UNITED STATES PATENTS 3,283,708 11/1966 Yackel Z50-65.1 3,298,833 1/1967 Gaynor 96-27 3,315,598 4/1967 Owen Z50- 65.1 3,392,020 7/ 1968 Yutzy 250-65.1 3,405,265 10/ 1968 Vrancken Z50-65.1

NORMAN G. TORCHIN, Primary Examiner J. R. HIGHTOWER, Assistant Examiner U.S. CI. X.R.

117-34, 35.5, 35.6, 36.1, 36.7; lOl-470; Z50-65.1 

